A simple perl plugin that allows nagios to check the rate of change of the output of any command as long as it's a number, e.g. filesystem usage growth, network traffic spikes, dns queries spikes, etc
It uses a sqlite3 database to store the last value.

The plugin executes the command specified by the user and stores it's output value in a sqlite3 database using the command's md5 hash as key.
The next time it's run it compares the new value with the old one, calculates the rate and updates the value in the database.
It can calculate the rate on a second, minute or 5-minute period.
After installing it change the database path if needed.
my $dbfile = '/usr/local/nagios3/var/check_rate_data.db';